The use of rotary immersion vibrators to compact unset concrete has long been known. Typically, such vibrators are immersed into concrete which has been poured into forms to build sidewalks, patios, roads, ramps, bridges and the like, so that the concrete can be vibrated to eliminate voids and air to avoid the formation of undesirable pockets or honeycombs, thereby increasing the structural strength of the concrete.
It is common for such vibrators to have a generally tube shaped housing enclosing a rotating eccentric weight that is driven by a flexible shaft or a hydraulic motor to generate vibrations. It is also common for the rotating eccentric weight to be straddle-mounted by rolling element bearings located at either end of the eccentric weight to transfer the oscillating radial loads from the eccentric weight to the tubular housing.
Typically, due to the relatively large radial loads generated by the rotating eccentric weight, the largest possible frame size for the bearings is used within the limited envelope provided by the tubular housing of the rotary vibrator.
Bearing failure is a problem frequently encountered in such vibrators due to the large per bearing operating loads which must be carried by the bearings at either end of the eccentric weight and due to the vibrator's limited ability to retain adequate lubrication in the bearings. Because of the straddle mounted configuration, the operating loads typically must be split between the two bearings at either end of the eccentric weight. Adding additional bearings at either end of the eccentric weight undesirably increases the length of the vibrator and has only a limited effect on the per bearing operating load due to the deflections of the eccentric weight at the bearing mount locations. Additionally, the straddle mounted configuration does not lend itself to retention of lubrication within the bearings because a seal is required on both sides of each bearing location at either end of the eccentric weight, resulting in four rotating seals.
Whenever a bearing fails, the vibrator and its associated equipment must be shut down and the vibrator must be extracted from the concrete and disassembled so that the bearing may be replaced. Commonly, the bearings, the eccentric weight, and the other elements of the rotary vibrator are stacked within the housing as separate components which, in many cases, must be extracted from the tubular housing one component at a time. This operation is not only time consuming, but introduces the risk that individual components may inadvertently fall from the tubular housing and become lost or damaged. After the bearing has been replaced, the vibrator must be reassembled and reinserted into the concrete for operation. Bearing failures have become increasingly problematic as the industry moves toward using dryer mixes of concrete to achieve higher structural strength. Dryer mix concrete requires higher vibratory forces in order to be adequately compacted. Thus, rotary vibrators are increasingly operated so as to achieve these higher vibratory forces, thereby resulting in an increased number of bearing failures.
There is a need for a new and effective rotary vibrator having an eccentric weight mount configuration which minimizes the per bearing operating loads, maintains adequate lubrication within the bearing to prevent untimely bearing failure, and provides for easy and quick bearing replacement when bearing failure occurs.